A Nov. 8 Science Notebook item incorrectly said that Jupiter has four moons. Jupiter has four large moons, but about 60 known moons in all. (Published 11/10/04)

Triple Eclipse Dots Jupiter

NASA last week released a Hubble Space Telescope image of a rare triple eclipse of the planet Jupiter by three of its four moons: Io, Ganymede and Callisto.

The picture shows Jupiter as a large sphere in pastel bands of rose, royal blue and chartreuse. The human eye would not see the planet in the same colors, planetary scientist Erich Karkoschka said, because the image was taken by infrared cameras.

The three shadows and two moons dot the picture of Jupiter like freckles. Io, whose surface is rich in sulfur compounds because of volcanic activity, appears as a white dot in the center of the image. Its shadow is the small black dot to its left.

Ganymede is the blue dot in the upper right, and its shadow is cast on the planet's far left edge.

The third shadow, on Jupiter's upper right edge, is Callisto, Jupiter's outermost moon. Callisto itself is out of the picture to the right. The picture was put together from images taken last March.

Karkoschka, a researcher at the University of Arizona's Lunar and Planetary Laboratory, said the triple eclipse is "easy to predict" because of the rhythm of the moons' orbits. The rhythm, however, makes it impossible for all four moons -- the fourth is Europa -- to produce an eclipse at the same time.

The triple eclipse happens about once a decade, Karkoschka said. The last one occurred in 1997. Seeing moons along with shadows is much rarer, occurring once every several decades, he said.

-- Guy Gugliotta

Pollution, Artery Disease Linked

Air pollution may cause and accelerate artery disease by helping to narrow carotid arteries, according to a study a University of Southern California professor presented yesterday at the American Heart Association's annual conference in New Orleans.

Nino Kuenzli, associate professor in the environmental division at USC's Keck School of Medicine, said his team analyzed data from two clinical trials of 798 Los Angeles residents who were at least 40 years old to determine how fine-particle pollution produced by power plants, automobiles and other sources causes artery damage.

After adjusting for several factors including smoking and age, the scientists concluded that an increase of 10 micrograms per cubic meter in fine-particle pollution led to an increase of as much as 4.3 percent in the thickness of artery walls. Such thickening can lead to calcification and ruptures, which block blood flow to the heart and cause heart attacks.

"We knew that people in more polluted areas die earlier from cardiovascular disease, but it was not clear how early in the disease process air pollution contributes," Kuenzli said. "Our study found that air pollution may contribute to cardiovascular problems at a very early stage of the disease, similar to smoking, and enhances atherosclerosis, which is the underlying disease process of cardiovascular diseases. It's speeding up the aging process."

-- Juliet Eilperin

Spirit, Opportunity Plug Away

The Mars rovers Spirit and Opportunity are still going strong after nearly nine months of exploration, overcoming wear and tear to scale a mountain on one side of the planet and plow deep into a valley on the other.

Ray Arvidson of Washington University, in St. Louis, the deputy lead scientist for the NASA mission, said in a briefing last week that Spirit's investigations on the slopes of the "Columbia Hills" suggested that the formation was created by volcanic activity.

The Columbia Hills -- about 300 feet high and four miles long -- are an older geological outcrop rising out of the younger plain where Spirit landed in January. Spirit has problems with its wheels but is able to function normally, Arvidson said. The rovers were designed to operate for three months.

Opportunity is on the other side of the planet exploring "Endurance Crater" and is heading briskly uphill toward "Burns Cliff," an exposure of layered sedimentary deposits, after bogging down for several days in deep sand and dust drifts in the crater bottom.

Rover project manager James K. Erickson, of NASA's Jet Propulsion Laboratory, said Opportunity had benefited from a pair of mysterious "cleaning events" that appeared to have removed dust from the solar arrays, enabling the batteries to charge to 80 percent of their original capacity. Spirit's arrays, by contrast, will charge to only 35 percent of capacity.

Cornell University's Steven Squyres, lead scientist for the expedition, said the team suspects that dust devils may have cleaned Opportunity's arrays, but efforts to catch them in the act with the rover's cameras had proved fruitless.

-- Guy Gugliotta

Five dots -- three black shadows and two moons, one white, one blue -- mark a triple eclipse of Jupiter in an image taken with the Hubble Space Telescope.